Well, as a last resort, wrap a 30 or so inch length of solder with wool yarn and stuff it inside the shaft. Instant heavy. I did this with an old Beeman hunter (the skinny shafts). It was around 1,100 grains.
There WAS a problem. The Beeman nocks were not strong enough to take the force of acceleration of that beast and two of them broke on release.
When the arrow hit the target, all of the barbs of the feathers bent forward.
I bet that thing would have fully penetrated a T Rex,
ChuckC